<p><strong>Abstract.</strong> August Colding was one of the three pioneers, who in the mid-1800s almost simultaneously and independently formulated the first law of thermodynamics, the two others being Robert Mayer and James Joule. This first, significant achievement was followed by a sequence of other ground-breaking discoveries within a broad range of disciplines: magnetism, steam power, gas production, hydraulics, soil physics, hydrology, heating and ventilation,

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... and oceanography. Moreover, he gave a significant contribution to the understanding of the spread of cholera. In hydrology, he used evaporation experiments to obtain water balances. Independently, he formulated Darcy's law, and, as the first one, he calculated the water table between drainpipes and the piezometric surface in confined aquifers. His main occupation, however, was chief engineer in Copenhagen, where he modernised the city by introducing groundwater-based water supply and building a waterworks delivering pressured, clean water into the houses, a gasworks and gas-based street lightening, and a citywide sewage system. Colding has not been recognised internationally as he might deserve, probably because most of his publications were written in Danish. Even in Denmark, he seems today almost forgotten. This paper highlights his most important scientific contributions, in particular his achievements in hydrology, hydraulics, meteorology and oceanography.</p>